1. Field of the Invention
The present invention relates to a projection display. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for enhancing color purity.
2. Discussion of the Related Art
Recently, a display device has a tendency for developing into its lightweight, slim size and wide screen, and more particularly, its lightweight and slim size become a matter of concern.
To achieve the light weight and slim size, a projection display instrument needs to employ a single panel illumination system using one display panel instead of employing a 3- or 2-panels illumination system using three display panels.
The single panel illumination system enables low price, lightweight and slim size which are smaller than those of the 3-panels illumination system. Yet, the single panel illumination system implements separation/synthesis of the three primary colors, red, blue and green of light by color sequential driving, thereby having radiation intensity lower than that of the 3-panels illumination system.
To supplement such a disadvantage of the single panel illumination system, color scrolling methods of implementing color by illuminating at least two kinds of color on a display panel instantly have been devised.
Yet, in the color scrolling type single panel projection display, at least two colors are simultaneously illuminated on one panel to implement colors. Hence, one color causes interference to an area of another color on the display panel to lower color purity.
For instance, blue and green lights intrude a red area to degrade red color purity. Likewise, a green or blue area is intruded by lights of the rest two colors to degrade its color purity. Such a color purity degradation always takes place in the color implementation system of the color scrolling method of implementing lights of at least two colors on one display panel simultaneously.
FIG. 1 is a diagram for explaining an example of occurrence of color intrusion at a random moment in case of implementing an entire screen with red in an illumination system of a single panel projection display device according to a related art, FIG. 2 is a diagram for explaining a color scrolling method by the rotating prism in a single panel projection display device according to a related art, and FIG. 3 is a diagram for explaining a color scrolling method by the color wheel in a single panel projection display device according to a related art.
A process that 1-color light intrudes an area of another color is explained with reference to FIG. 1 as follows.
FIG. 1 shows an example that green color intrudes red color in a color scrolling method of illuminating 2-color light on a panel at one arbitrary moment.
Referring to FIG. 1, white light projected from a light source 701 is homogenized and converted to a linearly polarized light having one optical axis by an integrator and polarizing converter 702 to proceed to a color separation unit 703. Any device operative in performing color separation by a color scrolling method can be used as the color separation unit 703. For instance, a color drum, a color wheel, a rotating prism or the like corresponds to the color separation unit 703. Namely, the color separation unit 703 splits the white light into lights of R, G and B areas. And, it is also assumed that the polarizing converter 202 converts the white light to a P-wave polarized light.
The R, G and B lights split by the color separation unit 703 are sequentially illuminated on a display panel 706 via an illumination lens array 704 and a PBS 705.
In FIG. 1 that shows an example of implementing an entire image by red color, an ON signal is applied to an area of the display panel having the red light illuminated thereon and an OFF signal is applied to an area of the panel having the green and blue lights applied thereto, in the color scrolling method. According to a time basis, the R, G and B lights, as shown in FIG. 2 and FIG. 3, then sequentially propagate. In doing so, the red light proceeds to a projection lens 707 via a PBS 705 only but the green and blue lights fail in proceeding toward the projection lens 707.
Namely, as the P-polarized red light is illuminated on the ON area of the display panel only, a polarized direction of the red light is converted to an S-wave from a P-wave to reflect to the PBS 705.
It is assumed that the PBS 705 is coated with a polarizing film to reflect the S-wave thereon and to transmit the P-wave therethrough.
If so, the S-wave red light is reflected by the PBS 705 toward the projection lens 707. The projection lens 707 then enlarges and projects the red light reflected by the PBS 705 to a screen (not shown in the drawing).
Meanwhile, the P-polarized green and blue lights, which are illuminated on the OFF area of the display panel, are reflected toward the PBS 705 without changing their polarized direction. Namely, the green and blue lights maintaining the P-polarization to be reflected toward the PBS 705.
For convenience of explanation, the green light among the green and blue lights is explained in detail as follows.
First of all, the green light, which is reflected by the OFF area of the display panel 706 to the PBS 705 to be in the P-polarized state G_p, is transmitted through the PBS 705 to enter the illumination lens array 704 as it is.
In doing so, it may happen that a portion G_p of the green light indicated by a dotted line in FIG. 1 is reflected by a random surface of the illumination lens array 704 to arrive at the red area of the display panel via the PBS 705. Since the panel signal of the red area is ‘ON’, the P-polarized green light G_p is converted to the green light G_s to reflect to the PBS 705. Since the PBS 705 is coated to reflect the S-polarized light, the S-polarized green light G_s is reflected by the PBS 705 to the projection lens 707. The projection lens 707 then enlarges to project the S-polarized green light to the red area of the screen.
Meanwhile, the blue light, on which the same process of the green light is carried out, is enlarged to be projected on the red area of the screen as well.
However, in case of the related art single panel projection display device enabling color implementation by illuminating at least two kinds of lights on the display panel simultaneously, the above-explained color intrusion degrades the quality of color image.